People always seem to associate Warlord with Life, but when you think about it, it maybe makes more sense in a Sorcery build.
Sorcery basically makes your units invulnerable to magic, and capable of rapid travel and such, but what it doesn't do is provide any way to really enhance the damage that your units can do. Warlord does this. Life can buff heroes and normal units already, so the effect of Warlord isn't as dramatic, but for Sorcery, where there is basically no other way to enhance unit performance, it's a more potent effect.
Life and Sorcery both tend to depend a lot on heroes and normal units, and both benefit from Warlord. Really I'd say that Sorcery is more dependent on heroes than Life and if you don't have Heroism then getting heroes started is often difficult. Warlord helps to address that issue.
Sorcery basically makes your units invulnerable to magic, and capable of rapid travel and such, but what it doesn't do is provide any way to really enhance the damage that your units can do. Warlord does this. Life can buff heroes and normal units already, so the effect of Warlord isn't as dramatic, but for Sorcery, where there is basically no other way to enhance unit performance, it's a more potent effect.
Life and Sorcery both tend to depend a lot on heroes and normal units, and both benefit from Warlord. Really I'd say that Sorcery is more dependent on heroes than Life and if you don't have Heroism then getting heroes started is often difficult. Warlord helps to address that issue.